Leaf domatia in montane forest and Caatinga in the semiarid of Pernambuco State: Morphology and ecological implications

Leaf domatia are cavity-shaped structures of different types or tufts of hairs located at the junction between ribs on the abaxial surface of the leaf blades of various families of angiosperms, serving as protection against phytophagous organisms by harboring beneficial mites, suggesting a mutualistic relationship. There is shortage of inventories of species with such structures; thus the present study examined native woody plant in two habitats of the backwoods of Pernambuco to identify the types of leaf domatia. 86 species were observed, 43 in Caatinga area, out of which five had domatia, and 43 in the montane forest, 11 species with domatia. Four types of domatia were observed: hairtufts, pocket, pit and revolute margin. There was predominance of plant species with leaf domatia in the area Carro Quebrado in Triunfo, Pernambuco State. These results corroborate the information available in the literature in which domatia are prevalent in more humid environments, and that these structures as micro-habitats influence the maintenance of diverse organisms.

Despite the mutualistic relationships between domatia and beneficial mites being quite old (LUNDSTROEN, 1887), it has long been left out, and most researchers have given these structures just a taxonomic character, not reporting the occurrence of arthropods inside.The domatia occur mainly in plants of humid environments and any physiological function for them has been mentioned (NAKAMURA et al., 1992;NORTON et al., 2000).
From the 1980s, research on the interaction between mites and leaf domatia took off and the mutualistic relationships were again discussed, culminating in a series of studies aiming at proving it (AGRAWAL et al., 2000;ENGLISH-LOEB, 2002;GROSTAL;O'DOWD, 1994;KARBAN et al., 1995;MATOS et al., 2004MATOS et al., , 2006;;O'DOWD;WILSON, 1989;PEMBERTON;TURNER, 1989;SCHICHA;O'DOWD, 1993;WALTER;O'DOWD, 1997).However, these studies have not emphasized the characterization of these structures and there is little information available in the literature on plants that have domatia on their leaves.
This study conducted a survey of leaf domatiabearing plants in two environments representing distinct vegetation formations in the Brazilian semiarid region (Caatinga and montane forest) and the types of domatia present in these plants, so as to provide a basis for ecology studies and interaction of these structures with small arthropods.

Material and methods
The study was conducted in two distinct environments, located in the semiarid region of Pernambuco State: a) Mata da Pimenteira (Caatinga area) -located in the Parque Estadual Mata da Pimenteira (7°53'49"S 38º18'14"W), municipality of Serra Talhada, Pernambuco State, Brazil.The altitude in the county ranges around 500-800 m (FERRAZ et al., 1998) and the annual rainfall between 600 and 700 mm; the average temperature is 26ºC (EMBRAPA, 2000) with hot semiarid climate.The vegetation is classified as deciduous forest, subjected to two well-defined seasons, drought, when most individuals lose their leaves, is prevalent (VELOSO et al., 1991).The area has a well preserved tree layer, rarely seen in the Caatinga, with individuals up to 18 m high being recorded (personal communication, Melo, A.).
It is located at 620 m altitude.The climate is hot and humid in Triunfo, rainfall around 1,222 mm and 25ºC average temperature (CPRM, 2005).This municipality is located in the city of Carro Quebrado about 20 km from a shopping center, where there is a well-preserved hillside vegetation consisting of tall trees, sometimes exceeding 25 meters in height (personal communication, Melo, A.).
Species Selection: phytosociological surveys previously performed in the study areas were used in this stage, considering species in which at least one individual met the diameter inclusion criteria at soil level greater than or equal to 3 cm and height greater than or equal to 1 m in plots of 10 x 10 m, totaling 0.5 ha in the Mata do Carro Quebrado (unpublished data) and 10 x 20 m totaling 0.8 ha in the Mata da Pimenteira (Farias, unpublished data).
The frequency of species occurrence in the two areas was verified based on the following criteria: 10 or more individuals -common species; two to nine individuals -occasional species and, one individualrare species in the study area.
Under stereomicroscope, each plant sample was evaluated for the presence/absence of leaf domatia, types of domatia found and location of these structures on leaves.The domatia classification was based on Barros (1961) and O' Dowd and Wilson (1989).The following types were found: (1) hairtufts; (2) pockets; (3) pits; (4) revolute margin.

Results and discussion
In each of the areas 43 species (Table 1) belonging to 33 families and 62 genera were recorded.Out of the 84 specimens examined, only 13 showed leaf domatia (Table 1) (Figures 1, 2 and 3); five recorded in the Mata da Pimenteira (corresponding to 5.81% of the total number of specimens from the area) and 11 in Mata do Carro Quebrado (corresponding to 22.05% of the total number of specimens from the area); Guettarda angelica Mart.ex.Müll.Arg. and Parapiptadenia zehntneri (Harms) M. P. Lima and H. C. Lima were present in both areas.
The domatia varied in type and position on the leaf.Four types of domatia were observed: hairtufts, pocket, pit and revolute margin.The type tufts of hairs predominated, occurring in seven species; the types pocket, fringe and pit appeared in four, two and one species respectively.
The greatest number of species with domatia in the Mata do Carro Quebrado (11 species) compared to Mata Pimenteira (5 species) is a significant result because the first area is a comparatively wetter environment than Mata da Pimenteira, which corroborates the information available in the literature, emphasizing that domatia are found mainly in plants of humid sites (NAKAMURA et al., 1992;NORTON et al., 2000).Only two species occur in both environments (Guettarda angelica and Parapiptadenia zehntneri).
Parapiptadenia zehntneri from Mata do Carro Quebrado showed conspicuously larger volume of hairs (trichomes) than that from Mata da Pimenteira, which can be easily observed in Figures 2 (A) and 3 (A).This fact is relevant to interaction studies, once according to Matos et al. (2011), variations in the density of trichomes can be decisive for the occurrence of phytophagous and predatory mites on plants.

Conclusion
The greater predominance of plant species with leaf domatia in the area Carro Quebrado in Triunfo, Pernambuco State, (most types pocket and hairtufts) compared to the area of Mata da Pimenteira in Serra Talhada, Pernambuco State, (most types hairtufts) can be explained by the fact that it is more humid which, according to the data available in the literature represents an environment of higher occurrence of plants with these characteristics.